Generally, there are three piston rings used in a cylinder of an internal combustion engine: the top ring, the second ring, and the oil ring. The three piston rings are positioned around a piston which reciprocates within the cylinder. The top ring, the second ring, and the oil ring are respectively spaced in vertically descending order around the walls of the piston The combination of all three piston rings serves to isolate the combustion chamber from the crankcase.
The top ring serves two purposes: preventing gases (from the combustion chamber) from passing therearound, and transferring heat from the piston to the engine block through the walls of the cylinder. The oil ring prevents oil (from the crankcase) from passing therearound. The second ring compliments both the top ring and the oil ring. The second ring prevents gases (which bypassed the top ring) from passing therearound, and prevents oil (which bypassed the oil ring) from passing therearound. Consequently, the top ring, the second ring, and the oil ring are seals for preventing the passage of gases and/or oil. Without the isolation of the combustion chamber and the crankcase provided by the piston rings, the presence of gases in the crankcase and oil in the combustion chamber would decrease the horsepower of the internal combustion engine.
To serve as seals, the top ring and second ring springingly engage the walls of the cylinder. For example, in the “free state” before installation, the top ring and second ring are biased to expand. That is, the top ring and second ring have expanded diameters forming a gap between their respective ends. When the top ring and second ring are installed around the piston, the ends of each ring are squeezed together. Thereafter, the piston and the surrounding rings are inserted into the cylinder. Because each ring is biased to expand toward its “free state,” the top ring and the bottom ring expand against the walls of the cylinder. As such, the top ring and the bottom ring springingly engage the walls of the cylinder, and serve to effectuate the above-discussed seal between the combustion chamber and the crankcase.
For normal use, it is generally unnecessary to “fit” the gaps between the ends of the top ring and the second ring to precise tolerances. However, for high performance/racing applications, fitting the gaps can be used to provide a competitive advantage. For example, the top rings and the second rings used in racing applications are often sold with oversized dimensions, and, therefore, provide small gaps between their ends. Consequently, before installation, the ends of the top rings and second rings can be filed and refiled to provide gaps of different sizes. Such different sized gaps provide for different separations between the ends when the piston rings are installed.
The filing and refiling allows the performance of the various gap sizes (and corresponding separations) to be tested, and such experimentation can enhance the performance of an internal combustion engine. For example, because internal combustion engines used in racing operate at high temperatures, it is necessary to provide a gap allowing for expansion of the piston rings according to the high temperatures. Thus, a properly sized gap would allow the ends to be initially separated when the piston rings are inserted into the cylinder, which separation could thereafter close when the piston rings expand due to exposure to high temperatures.
However, if the gaps are sized too small, the ends will close before the piston rings are finished expanding, and the piston rings will warp, thereby causing “scuffing” of the walls of the cylinder. Moreover, if the ends are misaligned, the ends will touch unevenly, which will not only cause unwanted separation therebetween before the piston rings are finished expanding, but which might also force the piston rings to expand awkwardly, thereby also causing “scuffing” of the walls of the cylinder. Consequently, the gaps must be precisely sized, and the ends must be properly aligned with respect to one another.
Thus, the user must first measure the gap between the ends of the ring and then, assuming that the gap is too small, must then grind the ends of the ring in an attempt to obtain the desired gap. A typical desired gap is 0.003 inch per inch of diameter of the cylinder, and as a result of working with such a precise number, oftentimes the measuring/grinding steps are repeated many times until the precise desired gap is obtained.
One of the problems with this procedure is the manner in which accurate measurements can be obtained so that the user knows how much grinding might be required and also knows when he has completed the project with the gap being at the desired size. One method of measuring the gap would be to insert the ring in a bore and attempt to measure the size of the gap. However, the user could never be certain whether the ring was perfectly perpendicular to the axis of the bore, because if it would not be perpendicular, it would be canted and inaccurate measurements would be obtained.
In an attempt to solve this problem, a device known as a squaring tool has been developed. This device consists of a ring of a known diameter (simulating the diameter of a piston) having a shoulder extending outwardly therefrom. The piston ring to be sized is placed around the ring and on the shoulder, and the gap may be measured. However, such a device is only good for one size of a cylinder bore, and since the diameter of the bores of typical cylinders range from 3.75 inches to 4.65 inches, numerous sizing rings encompassing a wide variety of piston diameters would have to be inventoried by the user.
As a result, the need exists for a device which can assist the user in accurately measuring, or otherwise checking, the size of the gap of a piston ring for a wide range of cylinder bore diameters.